The invention relates to a data processing circuit.
U.S. Pat. No. 5,367,638 discloses a circuit containing electronic circuitry including self-timed elements. Such electronic circuitry does not require a central clock to initiate operations. Instead, each self-timed element starts operating in response to its own local "request" signal received from a circuit that has to operate before the self-timed element, for example because it produces the data upon which the self-timed element operates. A self-timed element receives a request signal and starts operating only when it is necessary that the self-timed element operates. This is in contrast to centrally clocked circuit elements, which receive clock signals irrespective of whether they need to operate. Thus circuitry with self-timed elements consumes less power than centrally clocked circuit elements.
U.S. Pat. No. 5,367,638 moreover discloses a further reduction in power consumption which is achieved by regulating the supply voltage of the electronic circuitry, and thereby both its power consumption and its operating speed, so that the self timed elements complete operation just in time to cope with the processing load, but no faster.
The circuit of U.S. Pat. No. 5,367,638 has to accept and/or deliver data in real time, as defined by an external clock. In order to satisfy this real-time requirement with self-timed elements, the circuit contains a FIFO buffer which accepts data at the instants in time that the data is produced by the self-timed elements, buffers the data and outputs it at the instants time required according to the external clock. The speed of the circuit is regulated so that the FIFO buffer does not overflow.
The usefulness of this mechanism of realizing real-time performance is limited to the real-time production of data. Other real-time requirements, such as those which occur during execution of a program with instructions of which some (e.g. peripheral control instructions, refreshing access to DRAM) have to be executed with a specified time-delay with respect to each other, or with an specified average time-delay, cannot be satisfied in this way.
Amongst others, it is an object of the invention to provide for a circuit with a self-timed instruction execution unit with which real-time requirements can be satisfied.